Various tests are conducted for the purpose of identifying and discarding those IC packages that do not meet the required specifications for newly manufactured semiconductor integrated circuits. The burn-in procedure tests the IC's heat resistance properties by causing them to perform for a certain period of time at high temperature, thereby making it possible to cull out those that do not meet the required specifications. In a burn-in test, the IC is mounted on the socket that has been prepared exclusively for that purpose and the socket is in turn mounted on a printed circuit substrate for placement in a heating oven. Various kinds of sockets have been proposed for use in burn-in tests of IC packages of the LGA (Land Grid Array) or BGA (Ball Grid Array) types which have become popular in recent years. Basically, such sockets have a base member made of an insulating material and have a plurality of contact members that correspond to the terminals arranged on one surface of the IC. The contact members are arranged on the seating surface of the socket to correspond to each terminal of the IC to be brought in touch with the same when the IC has been placed on the seating surface. In a typical kind of socket, a cover is provided for holding the IC on the seating surface, with the IC being held on and removed from the seating surface by moving the cover up and down.
With reference to FIGS. 13 and 14, one such prior art socket has one side of a cover 142 rotatably supported on a base 141. When cover 142 is opened as shown in FIG. 14, IC 100 is placed onto seating surface 141a and cover 142 is closed by means of an automatic unit, not shown in the drawing. A hook 143 is engaged with a latch on base 141 to maintain cover 142 in a closed position. IC 100 on seating 141a is compressed from above by a compression surface 142a inside cover 142, with the terminals of the IC brought into engagement with the tip of respective contact members.
A problem with this type of socket is that when closing cover 142, compression surface 142a approaches the base in a way which is inclined Is relative to IC 100 with a result that a bias load is applied to the IC. This biased load can damage the IC itself and, at the same time, can result in an uneven compressive force of the contact elements 144 against the terminals of the IC. In addition, the construction of the automatic unit for the switching action of cover 142 is complicated.
Another type of prior art socket is equipped with a mechanism for the vertical movement of the cover member relative to the base member and a latch that opens or closes in linkage with the movement of the cover. It is generally the case that the latch opens when the cover member is lowered, thereby making it possible for the IC to be placed on the seating surface of the base and closes when the cover member is elevated, thereby making it possible for the IC on the seating surface to be held from above.
This type of socket is subject to the following limitations:
(1) The latch needs to have its holding portions extend onto the upper surface of the IC when it is closed and recede from the upper surface of the IC hen it is opened. In order to realize this mechanism, usually a latch and a driving mechanism therefor are arranged around the seating surface of the IC. Because of this, there is a tendency to increase the external size of the socket.
(2) This type of socket for use in burn-in tests has a comparatively large number of parts requiring much time for its assembly.
(3) In this type of socket, the contact members have a curved part pressed against the terminals of the IC with a spring force based on the bending of the curved part when they are pressed. Along with an ever-increasing density of the IC terminals, there is a concomitant demand for the socket to have a contact member with high connective reliability.